Drive assisting system

ABSTRACT

An object of the present invention is to provide a driving assistance system capable of displaying a picked-up image near a vehicle as a less-distorted image on a monitor.  
     A driving assistance system according to the present invention comprises an imaging means ( 2 ) for picking up a surrounding image of a vehicle ( 1 ) on a road surface, an image translating means ( 3 ) for executing an image translation by using a three-dimensional projection model ( 300 ), which is convex toward a road surface side and whose height from the road surface is not changed within a predetermined range from a top end portion of the vehicle ( 1 ) in a traveling direction, to translate the image picked up by the imaging means ( 2 ) into an image viewed from a virtual camera ( 2   a ), and a displaying means ( 4 ) for displaying an image translated by the image translating means ( 3 ). The three-dimensional projection model ( 300 ) is configured by a cylindrical surface model ( 301 ) that is convex toward the road surface side, and a spherical surface model ( 302 ) connected to an end portion of the cylindrical surface model ( 301 ). Accordingly, the straight line on the road surface, which is in parallel with the center axis of the cylindrical surface model ( 301 ), is displayed as the straight line, and thus a clear and less-distorted screen can be provided to the driver.

TECHNICAL FIELD

[0001] The present invention relates to a driving assistance systemwhich assists when a vehicle backs by displaying a vehicle rear-sideimage picked up by a camera equipped with the vehicle on a monitorequipped with the vehicle and, more particularly, to a drivingassistance system which displays a less distorted image on the equippedmonitor thereby not causing a driver to feel a sense of incompatibility.

BACKGROUND ART

[0002] A driving assistance system which installs an equipped camerabackward in a rear trunk portion or the like of a vehicle and providesan image of a rear side of the vehicle picked up by the equipped camerato the driver is spreading nowadays. Some of the driving assistancesystems translates/synthesizes a real image picked up the equippedcamera into an image that looks as if such image is picked up from aviewpoint being set virtually and displays a resultant image on amonitor, and the driving assistance systems are mainly used for thepurpose of the safety check and the parking assistance in backing thevehicle.

[0003] As a three-dimensional projection model used tosynthesize/translate the image, for example, as shown in FIG. 10, athree-dimensional projection model 100 configured to have a cylindricalsurface model 101 and a flat surface model 102 is used. Then, a realimage picked up by a real camera 103 is translated/synthesized into animage viewed from a virtual camera 104, and then is displayed as animage projected onto the three-dimensional projection model 100 on anequipped monitor.

[0004]FIG. 11 is an explanatory view showing an image obtained byprojecting a straight line 105 shown in FIG. 10 onto thethree-dimensional projection model 100. A straight line image 105 a on amonitor screen 106 is displayed to be folded at a model boundary 107between the cylindrical surface model 101 and the flat surface model102. In this manner, the reason for that originally straight line 105 istranslated as a folded image 105 a when the three-dimensional projectionmodel 100 configured to combine the cylindrical surface onto which thefar image is projected and the flat surface onto which the near image isprojected is used is that distortion of the display is concentrated ontothe model boundary 107 between two three-dimensional projection models101, 102. Thus, when the driver looks at this folded image 105 a, he orshe perceives a sense of incompatibility.

[0005] Therefore, if two three-dimensional projection models aresmoothly connected by a curved surface (third three-dimensionalprojection model), the straight line image 105 a is smoothly curved, asshown in FIG. 12, and it is possible to relax the sense ofincompatibility. However, since the distortion is concentrated onto aprojection surface 108 onto the third three-dimensional projectionmodel, a sense of incompatibility still remains.

[0006] Therefore, in the prior art set forth in JP-A-2002-83285, forexample, the three-dimensional projection model shown in FIG. 13 isproposed. This three-dimensional projection model 200 is configured tohave the cylindrical surface 101 onto which the far image is projected,and a spherical surface model 201 which is successively connected tothis surface and onto which the near image is projected. In this manner,since the spherical surface model 201 is used as the model on which thepicked-up image near the vehicle is projected, an overall projectedimage on the spherical surface model 201 changes smoothly and thereforea sense of incompatibility of the driver can be considerably relaxed.

[0007] However, if the above three-dimensional projection model 200shown in FIG. 13 is used, the picked-up image near the vehicle is neverdistorted at the particular portion concentrated, but it occurs aproblem that the distortion is generated in the overall image. Forexample, the image obtained by picking up an image of a lattice patternon the ground 202 by the real camera 103 and then projecting thepicked-up image onto the spherical surface model 201 is distorted as awhole, as shown in FIG. 14. That is, there is a problem such that agroup of straight lines constituting originally a lattice on the ground202 are displayed as a group of curved lines on the screen 106, and itis difficult to grasp positional relationships between the driver's ownvehicle and the surroundings based on such image.

[0008] An object of the present invention is to provide a drivingassistance system in which a three-dimensional projection model capableof monitoring/displaying a surrounding image of a vehicle as a lessdistorted image while suppressing incompatibility with a distant imagefrom the vehicle is installed.

DISCLOSURE OF INVENTION

[0009] In order to attain the above object, a driving assistance systemof the present invention has imaging means for picking up a surroundingimage of a vehicle on a road surface; image translating means forexecuting an image translation by using a three-dimensional projectionmodel, in which a shape on a side of the road surface is convex and aheight from the road surface does not vary within a predetermined rangefrom a top end portion of the vehicle in a traveling direction, totranslate the image picked up by the imaging means into an image viewedfrom a virtual viewpoint; and displaying means for displaying an imagetranslated by the image translating means.

[0010] According to this configuration, in the driving assistance systemof the present invention, the straight line such as the box of theparking lot, or the like depicted in parallel with the travelingdirection of the vehicle on the road surface near the vehicle isdisplayed as the straight line on the screen of the displaying means,and thus it becomes easy to grasp the relative positional relationshipbetween the driver's own vehicle and the surroundings.

[0011] Preferably, a projection surface that gradually gets up from theroad surface in a range extending beyond the predetermined range in awidth direction of the vehicle is continuously provided in thethree-dimensional projection model. According to this configuration, thepicked-up image in a wide range in the width direction of the vehiclecan be displayed on the screen not to make the image distortionprominent.

[0012] Preferably, a projection surface that gradually gets up from theroad surface in a range extending beyond the predetermined range in thetraveling direction of the vehicle is continuously provided in thethree-dimensional projection model. According to this configuration, thepicked-up image in a wide range in the traveling direction of thevehicle can be displayed on the screen not to make the image distortionprominent.

[0013] More preferably, the three-dimensional projection model is formedby successive curved surfaces that can be differentiated in a full rangeexcept end points. According to this configuration, no discontinuoussingular point is present on the screen, and a sense of incompatibilitycaused by connecting a plurality of three-dimensional models (thecylindrical surface and the spherical surface) is not generated. Also, ascale factor or a distortion can be varied on the screen by adjusting aninclination of the convex surface, and thus a sense of distance and asense of direction on the screen can be adjusted by utilizing this. Inaddition, since all three-dimensional models are a smooth curved surfacethat is convex downward, the image distortion is not concentrated into aparticular portion but dispersed over the entire screen to provide aclear screen. Therefore, the image by which the driver easily grasps thesense of distance and from which the driver does not feel a sense ofincompatibility can be provided to the driver.

[0014] More preferably, the three-dimensional projection model has acylindrical surface which shape on the side of the road surface isconvex, and a spherical surface which is smoothly connected to an endportion of the cylindrical surface. According to this configuration, thethree-dimensional projection models can be represented by equations, andthus the image translating process and formation of the mapping tablecan be made easy.

[0015] More preferably, the predetermined range is projected onto thecylindrical surface to has a length in the traveling direction of thevehicle, which is set to 120% or less of 5 m that is a length of anormal box of a parking lot, and a width, which is set to a range of 80%to 120% of 3 m that is a width of the normal box of the parking lot.According to this configuration, the screen that is suited to theparking operations can be provided to the driver.

[0016] More preferably, the cylindrical surface is a cylindrical surfaceof an ellipse, and the ellipse whose ratio of a maximum width and aminimum width between equal-interval lattice lines, which are inparallel with a center axis of the cylindrical surface on the roadsurface projected onto the cylindrical surface, is at least 80% in thepredetermined range is used as the three-dimensional projection model.According to this configuration, the screen that has a small distortioncan be provided to the driver.

[0017] More preferably, the three-dimensional projection model and aposition of the virtual viewpoint are set such that both left and rightends of a rear end image of the vehicle displayed on a screen of thedisplaying means enter into an at least 15% range of a screen width fromboth end positions of the screen. According to this configuration, theimage of the blind spot position, which cannot be directly viewed by thedriver, is displayed largely on the screen, and thus the driver candrive with a sense of security.

[0018] More preferably, the three-dimensional projection model and aposition of the virtual viewpoint are set such that a linear shape of arear end of the vehicle in the predetermined range is displayed as alinear image on the screen of the displaying means. According to thisconfiguration, the driver can easily confirm a shape of a bumper, etc.of the driver's own vehicle, and the driver can exactly grasped thepositional relationship between the road surface and the driver's ownvehicle. In addition, since positions of the three-dimensionalprojection model and the virtual viewpoint are set such that left andright both ends of the rear end image of the vehicle displayed on thescreen on the displaying means enter into an at least 15% range off thescreen width from both end positions of the screen, the image of therear portion of the vehicle such as the bumper, etc., which is displayedlarger than a width of the vehicle on the road surface on the screenobtained by the viewing translation, is cut off to have an appropriatewidth in response to the width of the screen and then displayed.Therefore, it is possible to reduce a factor of the sense ofincompatibility such that a width of the vehicle on the road surface anda width of the bumper are largely differently displayed.

[0019] More preferably, a guide line indicating a straight line on theroad surface, which is in parallel with the traveling direction of thevehicle and indicates an outer side that is outer than the width of thevehicle by a predetermined value, is superposed on an image translatedby using the three-dimensional projection model and to display on thescreen of the displaying means. According to this configuration, thedriver can intuitively catch the relative positional relationshipbetween the guide line and the straight line on the road surface fromthe screen, and thus the operation of aligning the position to the marksuch as the side line of the box of the parking lot, the road surface,etc. in the parking is made easy.

[0020] More preferably, the image translating means translates thepicked-up image by using a mapping table in which a translation addressbased on the three-dimensional projection model is stored. According tothis configuration, it is not required to execute the computing processby using the three-dimensional projection model every time, and thus theimage translating process can be carried out at a high speed.

BRIEF DESCRIPTION OF DRAWINGS

[0021]FIG. 1 is a configurative view showing a fitting of a drivingassistance system according to an embodiment of the present invention toa vehicle;

[0022]FIG. 2 is a configurative view showing details of the drivingassistance system according to the embodiment of the present invention;

[0023]FIG. 3 is a schematic view showing an image of a wide-angle camerapicked up by an imaging device in the driving assistance systemaccording to the embodiment of the present invention;

[0024]FIG. 4 is a schematic view showing an image obtained byeliminating a lens distortion from the image of the wide-angle camerapicked up by the imaging device in the driving assistance systemaccording to the embodiment of the present invention;

[0025]FIG. 5 is a schematic view showing a monitor display screen by thedriving assistance system according to the embodiment of the presentinvention;

[0026]FIG. 6 is a schematic view showing a variation of the monitordisplay screen by the driving assistance system according to theembodiment of the present invention;

[0027]FIG. 7 is an explanatory view showing a three-dimensionalprojection model used in the driving assistance system according to theembodiment of the present invention;

[0028]FIG. 8 is an explanatory view showing a three-dimensionalprojection model according to the embodiment of the present invention;

[0029]FIGS. 9A to 9C are explanatory views showing an example of animage translated by the three-dimensional projection model according tothe embodiment of the present invention;

[0030]FIG. 10 is an explanatory view showing a three-dimensionalprojection model used in the driving assistance system in the prior art;

[0031]FIG. 11 is a schematic view showing an image translated by thethree-dimensional projection model used in the driving assistance systemin the prior art;

[0032]FIG. 12 is a schematic view showing a variation of the translatedimage by the driving assistance system in the prior art;

[0033]FIG. 13 is an explanatory view showing another three-dimensionalprojection model used in the driving assistance system in the prior art;and

[0034]FIG. 14 is a schematic view showing an image distortion caused bythe three-dimensional projection model in FIG. 13 used in the drivingassistance system in the prior art.

[0035] In Figures, a reference numeral 1 is an own vehicle, la is abumper image, 2 is an imaging device, 3 is an image synthesizingtranslating system, 4 is a display device (monitor), 10 is adistance-indicating guide line, 11 is a width indicating guide line, 12is a linear guide line on a road surface, 21, 23 are cameras, 22, 24 areframe memories, 31 is an image synthesizing means, 32 is a mapping tablelooking-up means, 32 a is a translation address memory, 32 b is adegree-of-necessity memory, 33 is an image signal generating means, 300is a three-dimensional projection model, 301 is a cylindrical surfacemodel (ellipse), 302 is a spherical surface model (ellipse), 506 is aflat surface model, and 521, 522 are cylindrical surface models.

BEST MODE FOR CARRYING OUT THE INVENTION

[0036] An embodiment of the present invention will be explained withreference to the drawings hereinafter.

[0037]FIG. 1 is a configurative view showing a fitting of a drivingassistance system according to an embodiment of the present invention toa vehicle. This driving assistance system is configured to have animaging device 2 provided in a vehicle 1, an image synthesizingtranslating system 3 which processes an image picked up by the imagingdevice 2, and a monitor 4 which displays an image that was subjected tothe image synthesizing translating process.

[0038] The imaging device 2 is provided to pick up an image of the rearof the vehicle 1. A lens distortion is eliminated from the imageacquired from the imaging device 2 by the image synthesizing translatingsystem 3, and the image is translated into an image that looks as ifsuch image is picked up from any virtual viewpoint to display the imageon the monitor (displaying means) 4.

[0039]FIG. 2 is a configurative view showing details of the drivingassistance system. The imaging device 2 includes a camera 21 provided topick up an image of the left-side area on the back side of the vehicle,a frame memory 22 which temporarily holds image data obtained from thecamera 21, a camera 23 provided to pick up an image of the right-sidearea on the back side of the vehicle, and a frame memory 24 whichtemporarily holds image data obtained from the camera 23. In the presentembodiment, the left side and right side on the back side of the vehicleare picked up by the cameras 21, 23 respectively and then left and rightpicked-up images are synthesized. But, the left side and right side onthe back side of the vehicle might be picked up by one camera at a time.

[0040] The image synthesizing translating system 3 is configured to havean image synthesizing means 31 which synthesizes left-side andright-side images on the back side of the vehicle read from two framememories 22, 24 of the imaging device 2, a mapping table looking-upmeans 32 which stores mapping information of respective pixels of theimage that is synthesized by the image synthesizing means 31, and animage signal generating means 33 which translates the image synthesizedby the image synthesizing means 31 into an image signal.

[0041] The mapping table looking-up means 32 includes a translationaddress memory 32 a which stores translation addresses (a mapping table)indicating correspondences between positional coordinates of respectivepixels of an output image (an image displayed on the monitor 4) andpositional coordinates of respective pixels of input images (imagespicked up by the cameras 21, 23), and a degree-of-necessity memory 32 bwhich stores degrees-of-necessity of respective pixels of the inputimages.

[0042] Here, a “degree-of-necessity” is a value to calculate of additionwhen a sheet of output image is generated by connecting left-side andright-side input images, for example, such that a degree-of-necessity ofthe right-side input image is “0.5”, a degree-of-necessity of theleft-side input image is “0.5”, etc. when values of respective pixeldata of the area where the left-side and right-side input imagescombines each other are to be decided. Also, the above translationaddresses are previously generated on the basis of the three-dimensionalprojection model described later in detail, and stored in thetranslation address memory 32 a.

[0043] The image synthesizing means 31 generates data of the outputpixels by synthesizing respective pixel data in the frame memories 22,24 by mixers 31 a, 31 b according to the designated degree-of-necessitybased on the translation addresses (the mapping table) recorded in themapping table looking-up means 32, and then adding the synthesizedleft-side and right-side pixel data by an adder 31 c.

[0044] That is, the image synthesizing means 31 operates based on anappropriate synchronizing signal such as the input image signal, or thelike, for example, generates the output image by synthesizing the imagesinput from two different cameras 21, 23 in accordance with the mappingtable looking-up means 32 or changing respective pixel positions, andthus connects the input images input from plural different cameras 21,23 in real time or translates the input images into an image viewed fromthe virtual viewpoint.

[0045] The image signal generating means 33 translates output pixel dataoutput from the image synthesizing means 31 to the image signal, andoutputs the signal to the monitor 4.

[0046] The translation addresses stored in the mapping table looking-upmeans 32 are generated based on the three-dimensional projection modelaccording to the present embodiment. This three-dimensional projectionmodel is a model indicating correspondences when the images picked up bythe cameras 21, 23 are translated to the image that looks as ifsuch-image is picked up by the virtual camera which is installed at avirtual viewing position.

[0047] Actually, the cameras 21, 23 are wide-angle camera. The image onthe rear side of the vehicle, which can be obtained by synthesizing thepicked-up images laterally, is displayed as larger as the image iscloser to the vehicle and is displayed as smaller as the image isfurther from the vehicle, as shown in FIG. 3. The illustrated exampleshows the image of a parking area (normally a rectangular area whosevertical dimension is almost 5 m and whose lateral dimension is almost 3m is shown. This parking area is indicated by a lattice pattern to beeasy to understand.) of the rear of the vehicle, which is picked up bythe wide-angle camera. In the present embodiment, as shown in FIG. 5 andFIG. 6, the image in FIG. 3 is displayed on the monitor 4 as the clearand less-distorted image by the translation addresses generated by usingthe three-dimensional projection model described later.

[0048]FIG. 7 is a view showing a three-dimensional projection model usedin the present embodiment. A three-dimensional projection model 300 usedin the present embodiment is configured to include a cylindrical surfacemodel 301 on which the far image is projected, and a spherical surfacemodel 302 which is connected smoothly to the cylindrical surface model301 and on which the near image is projected. An alignment direction ofthis three-dimensional projection model 300 is different from theconventional three-dimensional projection model 200 explained in FIG.13. That is, the present embodiment is characterized in that an axis ofthe cylindrical surface model 301 is arranged in parallel with theground (road surface), i.e., the traveling direction of own vehicle 1,and a lower convex surface of the cylindrical surface model 301 isarranged on the ground side.

[0049] The imaging device 2 installed in the own vehicle 1 to pick upthe backward image picks up the backward image in the axial direction ofthe three-dimensional projection model 300. The image synthesizingtranslating system 3 translates the picked-up image picked up by theimaging device 2 into the image that looks as if such image is picked upby a virtual camera 2 a, which is installed over the actual imagingdevice 2, through the three-dimensional projection model 300, and thendisplays the image on the monitor 4.

[0050] The cylindrical surface model 301 of the three-dimensionalprojection model 300 is a semi-spherical model that is installed on theroad surface such that a center axis of the cylindrical surface model301 is in parallel with the traveling direction of the vehicle and iscut in half by a flat surface that passes through the center axis of thecylindrical surface model 301 in parallel with the road surface. Thespherical surface model 302 is a spherical surface whose radius isidentical to a radius of the cylindrical surface model 301, whose centeris on the center axis of the cylindrical surface model 301, and whosecut end formed by cutting the sphere by a plane, which passes throughthe center and has the center axis of the cylindrical surface model 301as a perpendicular, perfectly coincides with the cylindrical surfacemodel 301. That is, the cylindrical surface model 301 and the sphericalsurface model 302 can be differentiated at all points (except endpoints) on the boundary.

[0051] For convenience of explanation, the above three-dimensionalprojection model 300 is explained as a “circular cylinder” and a“sphere”. But the model is not always be a perfect “circular cylinder”and a perfect “sphere”, and may be as an ellipse, an elliptic sphererespectively. For example, the ellipse that is oblate on the roadsurface side may be selected as the three-dimensional projection model.A view showing by the three-dimensional projection model consisting ofthis ellipse, which is cut by a flat plane perpendicular to thetraveling direction of the vehicle 1, is FIG. 8. In this case, FIG. 8shows not only the lower half of the ellipse constituting the model butalso an overall ellipse.

[0052] Three three-dimensional projection models are shown in FIG. 8.One model is a flat surface model 506 whose direction coincides with theroad surface, and the other two models are elliptic models 521, 522whose ellipticity is respectively different (the portion correspondingto the three-dimensional projection model 301 in FIG. 7). Only a lengthof a minor axis is different between the elliptic models 521, 522. Viewsobtained by picking up an image of a lattice pattern, which is depictedon the road surface at an equal interval, by the imaging device 2 shownin FIG. 7, and then translating the image into an image that looks as ifsuch image is picked up by the virtual camera 2 a shown in FIG. 7through three models 506, 521, 522 shown in FIG. 8 are FIGS. 9A-9Crespectively. In this case, these images are picked up when the virtualcamera 2 a is directed just downwards.

[0053] As shown in FIG. 8, assume that an axis that is in parallel withthe center axes of the cylindrical surfaces of the ellipses 521, 522 andis positioned on the road surface is set as a Y axis, an axis thatintersects orthogonally with the Y axis and is perpendicular to the roadsurface is set as a Z axis, and an axis that intersects orthogonallywith the Y axis and the Z axis is set as an X axis, their values on theY axis are the same in respective models 506, 521, 522, but theirheights become different (values on the Z-axis direction) as theposition becomes more distant from the Y axis in the X-axis direction.

[0054] In other words, out of the lattice pattern depicted on the roadsurface, the lines that are in parallel with the Y axis are alsodepicted as parallel lines on the screens that are translated with usingrespective models 506, 521, 522. In the model 522 having a smallellipticity, i.e., in which a position goes away from the road surfaceas the position becomes more distant in the X-axis direction, aninterval x2 of the lattice pattern on the end side of the screen becomesnarrower than an interval x1 of the lattice pattern around the center,as shown in FIG. 9C.

[0055] Therefore, in the three-dimensional projection model 300 (thecylindrical surface model 521 of the ellipse shown in FIG. 8 is used asthe cylindrical surface model 301 of the actually used model 300, andthe spherical surface model of the ellipse being continued smoothly tothe cylindrical surface model 521 of the ellipse is used as thespherical surface model 302) used in the present embodiment, it isdecided as follows to what extent the ellipticity of the ellipse that isused as the cylindrical surface model 521 should be set.

[0056] That is, the X axis shown in FIG. 8 corresponds to the widthdirection of own vehicle 1 shown in FIG. 7. Therefore, any range 503 istaken out from a range of 80% to 120 of 3 m which is a width of a normalbox of a parking lot having the Y axis as its center. Then, thethree-dimensional projection model 521 of the ellipse is set such that aratio of a maximum value Xmax and a minimum value Xmin of the intervalof the lattice pattern, which is formed at an equal interval on the roadsurface, is at least 80% or more, as shown in FIG. 9B, within the imagethat is subjected to the translation through the three-dimensionalprojection model 521 contained in this range 503.

[0057] Such three-dimensional projection model 521 can be easily set byadjusting lengths of a major axis and a minor axis of the ellipse.,Views obtained by deciding the cylindrical surface model 301 in FIG. 7based on the ellipse in this manner and displaying the translated imageof the lattice pattern are FIG. 5 and FIG. 6. In these translatedimages, the straight line extending in the same direction as thetraveling direction of own vehicle 1 is also displayed as the straightline in the translated image, and the image distortion in the translatedimage along the width direction can be suppressed into the gentledistortion to such an extent that the driver does not feel a sense ofincompatibility.

[0058] In the driving operations of the vehicle, since the straightlines such as the side line of the road, the side line of the box of theparking lot, etc., which are in parallel with the Y axis, are often usedas a mark, it is a big advantage in the driving operations that thestraight line along the Y axis can also be displayed as the straightline in the translated image. In the present embodiment, since thecylindrical surface model 301 is employed as the model on which thepicked-up image of the road surface is projected, the straight line istranslated into the straight line. As a result, the present embodimentcan enjoy this advantage.

[0059] Meanwhile, in a far range 504 that extends in the width directionbeyond the range 503 shown in FIG. 8, if the picked-up image isprojected onto the flat surface, a solid body is largely distorted andthus the driver feels strange. Therefore, in order to reduce this imagedistortion, it is preferable that the projecting surface should be setas a surface that gets up from the road surface. However, if thisprojecting surface is set to a surface that suddenly gets up from thecylindrical surface model 301, the image distortion is concentrated ontothe boundary portion. Therefore, it is preferable that the projectingsurface getting up gradually should be selected. Since the ellipticmodel 521 gradually gets up in the range 504, the image distortion canbe dispersed over the entire screen by using this elliptic model 521 inthe range 504. Therefore, it is feasible to provide the translated imagethat causes the driver to feel less a sense of incompatibility.

[0060] This is similarly true of the Y-axis direction. If the farpicked-up image in the Y-axis direction is projected onto the flatsurface, the solid body is largely distorted and thus the driver feelsstrange. Therefore, it is also needed in the Y-axis direction that theprojecting surface is caused to get up in the far range. Since theY-axis direction corresponds to the traveling direction of the vehicle,i.e., the longitudinal direction of the vehicle, the image translationis executed in a predetermined range from the rear end of the vehicle byusing the model 521 whereas the image translation is executed in arange, which extends beyond the predetermined range from the rear end ofthe vehicle, by using the elliptic sphere (the model 302 in FIG. 7)continued from the model 521.

[0061] Since the normal box of a parking lot is 5 m in length, it isdesired that this predetermined range in the Y-axis direction should beset any value in 80% to 120% of a 5 m range. Also, it is preferable thatno inclination is provided to the Y-axis direction in this predeterminedrange. In the cylindrical surface model 301 of the three-dimensionalprojection model 300 according to the present embodiment, a height ofthe lowermost position from the road surface is set to zero (coincideswith the road surface) over the length of the cylindrical surface model301. Accordingly, the straight line in the picked-up image in thepredetermined range is also displayed as the straight line in thetranslated image.

[0062] However, in many case almost a half of the picked-up image by theimaging device 2 shown in FIG. 7 is located within an about 2 m rangefrom the rear portion of the vehicle. In such image, it is not alwaysneeded to keep above 5 m. An inclination may not be provided to theY-axis direction only within the 2 m range in which a sufficient spaceresolution is achieved, but the inclination may be gradually increasedin a range extending beyond 2 m, like the X-axis direction.

[0063] In the translated images in FIG. 5 and FIG. 6 according to thepresent embodiment, the straight line is displayed as the straight lineon this side of a distance-indicating guide line 10 indicating the 2 mrange from the rear portion of the vehicle, while the image translationis carried out by using the elliptic sphere model 302 in the rangeextending beyond 2 m. The predetermined range is different according tothe installation position of the imaging device 2, the resolution, theposition of the virtual viewpoint, etc. In this case, it is desired froma point of view of the driving assistance that the ellipse model 301should be applied in the box of the parking lot range from the rear endof the vehicle 1, which is selected as the predetermined range, and alsothe elliptic sphere model 302 should be applied in the farther range.

[0064] In the present embodiment, the three-dimensional projection modelis configured with the cylindrical surface model 301 as the ellipse andthe spherical surface model 302 as the ellipse. Accordingly, thecylindrical surface model 301 as the ellipse and the spherical surfacemodel 302 as the ellipse are continuously coupled. As a result, as shownin FIG. 5 and FIG. 6, the translated image is smoothly connected in theboundary surface between the model 301 and the model 302 of thethree-dimensional projection model 300. Thus, the driver cannotdiscriminate the boundary and never perceive a sense of incompatibility.

[0065] As described above, an extent of image distortion of the solidbody in the range 504 can be adjusted by adjusting the inclination ofthe projection model in this range 504 shown in FIG. 8. For example, asshown in FIG. 5, if an appropriate inclination is provided to theprojection model in the range 504, a distortion level of the imagepicked up by the imaging device using a wide-angle lens can be adjusted,so that a scale factor of other vehicle in a distant place can be set toget the sense of distance obtained when the driver actually looks out ofthe rear window.

[0066]FIG. 4 illustrated by way of comparison shows the image of awide-angle lens in FIG. 3 from which a lens distortion of the wide-anglelens is eliminated. It is appreciated that, even though only the lensdistortion is eliminated, an effect of emphasizing the sense of distanceby using the wide-angle lens is not relaxed. That is, a distant imagelooks more distant, the sense of distance is still emphasized in theimage. In contrast, in the present embodiment, since the far image istranslated by using the elliptic sphere model 302, the sense of distanceis relaxed to provide a clear image, as shown in FIG. 5.

[0067] If the major axes and the minor axes of the cylindrical surfacemodel 301 and the elliptic sphere model 302 in FIG. 7 and the viewingposition of the virtual camera 2 a are adjusted, the image shown in FIG.5 can be translated into the image shown in FIG. 6 and then displayed onthe monitor 4. That is, a width d of the own vehicle 1 on the roadsurface can be displayed on the screen in an enlarged fashion. In thisFIG. 6, the image shown in FIG. 5 is translated and displayed such thatboth end positions of the vehicle enter into a 15% range of the screenwidth from both end positions of the screen.

[0068] According to such enlarged display, the image near the rear endof the own vehicle 1, which is a blind spot of the driver, is displayedfully on the screen of the monitor 4. Therefore, it gives the driver asense of security. As a result, the driver can perform the drivingoperations with a sense of security.

[0069] Similarly, if the major axes and the minor axes of the ellipsesof the cylindrical surface model 301 and the elliptic sphere model 302in FIG. 7 and the position of the virtual camera 2 a are adjusted, abumper image 1 a of the own vehicle 1 can be displayed as the straightline, as shown in FIG. 5 and FIG. 6. Compared with that the bumper imagela is displayed in curve, as shown in FIG. 3 or FIG. 4, the driver feelsa sense of less-incompatibility to do the driving operations easily.

[0070] In addition, in the present embodiment, as shown in FIG. 6, forexample, a mark 11 indicating a width of the vehicle and a guide line 12corresponding to a straight line on the road surface, which indicates aside that is in parallel with the traveling direction of the vehicle andis positioned slightly outer than the width d of the vehicle, aredisplayed. According to these displays, the driver can intuitively graspthe mutual positional relationship between the side line of the road orthe box of the parking lot and the driver's own vehicle from the screento assist the exact driving operation.

[0071] In this case, the above three-dimensional projection modelconfigured with the cylindrical surface model and the spherical surfacemodel is not always configured by the curved surfaces that are definedby the equations, and decided based on the application range and theproperty. For example, the cylindrical surface model 301 as the ellipseis not always shaped into the elliptic shape in compliance with theelliptic equation. The three-dimensional projection model that is convexdownwards and is shaped to disperse the distortion of thetranslated-image over the entire image may be employed. The same isapplied to the spherical surface model 302.

[0072] The present invention is explained in detail with reference tothe particular embodiment. But it is obvious for the person skilled inthe art that various variations and modifications may be applied withoutdeparting a spirit and a scope of the present invention.

[0073] This application was made based on Japanese Patent. ApplicationNo.2002-171484 filed on Jun. 12, 2002, and the content thereof isincorporated hereinto by the reference.

[0074] <Industrial Applicability>

[0075] According to the present invention, it is feasible to provide thedriving assistance system that is capable of monitoring/displaying thesurrounding image of the vehicle as the less-distorted image.

1. A driving assistance system comprising: imaging means for picking upa surrounding image of a vehicle on a road surface; image translatingmeans for executing an image translation by using a three-dimensionalprojection model, in which a shape on a side of the road surface isconvex and a height from the road surface does not vary within apredetermined range from a top end portion of the vehicle in a travelingdirection, to translate the image picked up by the imaging means into animage viewed from a virtual viewpoint; and displaying means fordisplaying an image translated by the image translating means.
 2. Thedriving assistance system according to claim 1, wherein a projectionsurface that gradually gets up from the road surface in a rangeextending beyond the predetermined range in a width direction of thevehicle is continuously provided in the three-dimensional projectionmodel.
 3. The driving assistance system according to claim 1 or claim 2,wherein a projection surface that gradually gets up from the roadsurface in a range extending beyond the predetermined range in thetraveling direction of the vehicle is continuously provided in thethree-dimensional projection model.
 4. The driving assistance systemaccording to any one of claim 1 to claim 3, wherein thethree-dimensional projection model is formed by successive curvedsurfaces that can be differentiated in a full range except end points.5. The driving assistance system according to claim 4, wherein thethree-dimensional projection model has a cylindrical surface which shapeon the side of the road surface is convex, and a spherical surface whichis smoothly connected to an end portion of the cylindrical surface. 6.The driving assistance system according to claim 5, wherein thepredetermined range is projected onto the cylindrical surface to has alength in the traveling direction of the vehicle, which is set to 120%or less of 5 m that is a length of a normal box of a parking lot, and tohas a arbitral width, which is set to a range of 80% to 120% of 3 m thatis a width of the normal box of the parking lot.
 7. The drivingassistance system according to claim 5 or claim 6, wherein thecylindrical surface is a cylindrical surface of an ellipse, and theellipse whose ratio of a maximum width and a minimum width betweenequal-interval lattice lines, which are in parallel with a center axisof the cylindrical surface on the road surface projected onto thecylindrical surface, is at least 80% in the predetermined range is usedas the three-dimensional projection model.
 8. The driving assistancesystem according to any one of claim 5 to claim 7, wherein thethree-dimensional projection model and a position of the virtualviewpoint are set such that both left and right ends of a rear end imageof the vehicle displayed on a screen of the displaying means enter intoan at least 15% range of a screen width from both end positions of thescreen.
 9. The driving assistance system according to any one of claim 5to claim 8, wherein the three-dimensional projection model and aposition of the virtual viewpoint are set such that a linear shape of arear end of the vehicle in the predetermined range is displayed as alinear image on the screen of the displaying means.
 10. The drivingassistance system according to any one of claim 1 to claim 9, wherein aguide line indicating a straight line on the road surface, which is inparallel with the traveling direction of the vehicle and indicates anouter side that is outer than the width of the vehicle by apredetermined value, is superposed on an image translated by using thethree-dimensional projection model to display on the screen of thedisplaying means.
 11. The driving assistance system according to any oneof claim 1 to claim 10, wherein the image translating means translatesthe picked-up image by using a mapping table in which a translationaddress based on the three-dimensional projection model is stored.